Many people have difficulty distinguishing one color from another. This condition is called ‘color vision deficiency’, and is known colloquially as ‘color blindness’. Several different forms of color vision deficiency are recognized, including red-green dichromacy (protanopia, deuteranopia), anomalous red-green trichromacy (protanomaly and deuteranomaly), blue-yellow dichromacy (tritanopia) and anomalous blue-yellow trichromacy (tritanomaly). Each form is caused by the expression of a recessive genetic trait that reduces the variety of retinal cones in the affected person's eyes, or makes some of the cones less sensitive. Carried primarily on the Y chromosome, these traits may affect 7 to 10% of the male population, and about 0.5% of the female population. Total color blindness (monochromacy) is also recognized, as are injury-related color vision defects.
In society, color vision deficiency may cause some degree of disability. For example, it may tax an affected person's ability to decipher traffic signals or other signage. It may disqualify the person for employment in fields where acute color vision is required. Moreover, a color vision deficit may occlude the affected person's overall perception—and enjoyment—of the visual world. Unfortunately, there is no medical cure or treatment for color vision deficiency.